The Characteristics And Mechanism Of Karst Reservoirs In Tazhong Area Of Tarim Basin

The thesis aims at the practical demand of hydorearbon exploration of marinecarbonate rock in Tarim Basin.In this thesis,combining various kinds of methodsbased on theories of carbonate rock sedimentology,carbonate sequencestratigraphy,reservoir geology and depend on the techniques of seismics,drilling,logging,thin section,cathodoluminescence,scanning electron microscopy and analysisof reservoir geochemistry,Systematically studied the karst reservoir characteristicsand karst reservoir mechanism of the YingShan formation in Tazhong Area,andpredicted favorable areas of the karst reservoirs.Based on the theories of carbonate sedimentology and the material ofsedimentology rocks,Cores,thin sections and well logs,Sedimentary facies andmicrofacies of YingShan formation have been divided and show in the planepictures,Sedimentary sequences have been analysised vertically.and the depositionalmodel of YingShan formation in Tazhong Area was defined as limited platform-anopen platform-the platform margin-slope-basin.With the vail classic sequence stratigraphy theory as a guidance,through methodssuch as seismic,drilling and logging data to identify the sequence boundaries,identification signs including lithology mutation face,natural gamma abnormal surfacecharacteristics,and come to a conclusion that the sequences of YingShan Formationhave been divided into three third-order sequences,SQ1,mainly gray-light graydolomite deposition;SQ2,mainly gray limestone and dark gray limestone interbeddedsection,visible tidal-flat facies of shallowing-upward sedimentary characteristics;SQ3,gray particles limestone,micrite,visible shallowing-upward characteristics inbeach facies.On this basis,established the sequence stratigraphic framework,and in which the characteristics sequences have been analyzed.In accordance with the diagenetic stage and diagenetic environment,Carbonatekarst of the YingShan Formation in the Middle-Lower Ordovician have been dividedthree periods,includeing the syngenesis solution period,epigenetic kast and buriedsolution:①From the perspective of sedimentary facies,the study area of YingShanFormation identified the intra-platform beach and tidal flat during the syngenesissolution period,though a comprehensive analysis of cores,log interpretation and thinsections,recongnition symbols of syngenesis solution of the intra-platform beach andtidal flat,which is mainly considered as shallowing-upward cycles features insyngenesis solution period；②According to the characteristics of the core,FMI,strontium isotopes,carbon and oxygen isotopes,recongnized the symbols of theepigenetic karst,On the basis of the sequence stratigraphic theories,combined with theisopach map.In the study area the epigenetic karst paleogeomorphology have beendivied into three types,including karst highland,karst slope and karst valley.Karsthighlands mainly in the vicinity of Badong2well and of Zhong13well,Karst slopesmainly in the orientations toward north and west of the karst highlands,the traits ofKarst slopes is evidengtly in the Zhong15well and Zhong19well,karst valley in thestudy area development is not clear.The epigenetic karst have been divided into fourkarst phase belt vertically,including surface epikarst zone,vertical vadose zone andhorizontal phreatic zone and subcritical flow zone;③through the core,thinsections,scanning electron microscope observation and analysis,recongnized symbolsof the buried karst of the study area,including organic acids karst and hydrothermalkarst, the characteristics of organic acid fluid dissolution have been observed inZhong12well and Zhong16well,recongnized black asphalt and residual traces of oil;By scanning electron microscopy,Dissolution seam inside the cave,fillingfluorite,barite and other minerals have been found in the19well,13wells,15wells,saddle dolomite either been found.Studied the supergene karst mechanism of YingShan Formation of Tazhong areain the middle-Lower Ordovician,the characteristics of kast reservoirs related tointerfaces which included Middle Caledonian the screen （T74）,the middleCaledonian III screen（T70） the early Hercynian tectonic movement（T60）have beenanalysised,kast reservoirs is divided planely.Supergene karst mechanism wasanalyzed on many aspects which incluing ancient climate,ancient karst landform andbase-level cyclic change,and the kast cycle and kast caves evolution makes a briefdiscussion.It is considered in this thesis that syngenesis solution mechanism mainly is related to the beach type of atmosphetic fresh water lens and the regional freshwaterphase belt.That buried solution mechanism as follows: The hydrothermal dissolutionis mainly affected by temperature changes,structural fracture and the sequenceinterface to control the migration of hydrothermal fluids,using hydrothermal solutionTSR model and the backward for temperature to dissolve model to analysis the buriedkarst mechanism.Through analysis of epigenetic karst,syngenetic solution and buried solutionfeatures and dissolution mechanism,and established karst system graph of YingShanFormation in Tazhong area duing the middle-Lower Ordovician.On the basis oflithology,thin slices and physical property material,Reservoir space types of YingShanFormation included pores,dissolution pores,caves and fractures,There are three maindissolution reservoir types of YingShan Formation in the study area and they aredissolution pores type,dissolved pore-fracture type and fracture type,the two formerare the best reservoir types in the study area,and plane prediction the reservoirs.anddissolution reservoirs is predicted planely.